This invention relates to communication systems. More particularly, it is concerned with receiving apparatus for processing differential phase shift keyed (DPSK) signals.
Communication systems employing DPSK signals are well-known. Digital data is encoded in the signals by varying the phase of the carrier signal during succeeding signal periods or bauds. That is, the relationship of the phase of one signal to the phase of the preceding signal designates the digital data present in the one signal. In a binary phase system a single bit is encoded in each signal, and in a quadrature phase system two bits of data are encoded in each signal.
In receiving and decoding DPSK signals a reference point must be established with respect to the period of each signal in order to avoid signal transitions when sampling the signals. Time tracking arrangements for analyzing the received signals to determine a proper reference point during each signal have been developed and employed in DPSK communication systems. One typical arrangement employs circuitry for integrating two samples taken during the period of a received signal, comparing the results of integration, and adjusting the times of taking samples until the results are equal; thereby establishing a known reference with respect to the received signal periods. Time tracking arrangements of this general type, however, require many circuit components making them complex and expensive.